This application relates to the art of slitters and, more particularly, to slitters for slitting continuous sheet material into ribbons of precise width.
Slitting apparatus of a known type includes spaced and parallel rotatable shafts having cooperating cutting knives thereon. Sheet material is fed between the cooperating cutting knives which slit the sheet material into relatively narrow ribbons.
For certain applications, precision slitting of a sheet into ribbons is necessary due to the end use of the ribbons. For example, sheets of soft metal or the like are cut into ribbons for use as magnetic recording and playing tape. The magnetic tape is guided at its opposite edges through a playing and recording head, and the opposite longitudinal edges of the tape must not deviate from being parallel by more than hundredths of a millimeter.
In known slitters of the type described, the cooperating knife on the rotatable shafts are clamped axially. The end surfaces of the knives members and bushings cannot be machined perfectly flat, and some irregularities normally result. Axial clamping forces are also uneven for many reasons, and the central mounting hole in a knife member or bushing cannot be made perfectly perpendicular to its end surfaces. Even though defects of the type described may be only thousandths of a millimeter, they accumulate and combine with errors in final clamping or adjustment to cause defects in ribbons slit from sheet material by the knives.
In previous apparatus of the type described, sufficient axial clearance or movement has been provided between the cutting knives on the two shafts for accommodating the sum of all the irregularities and adjustment errors. As a result, the cutting gaps between the knives vary in size and axial position during each rotation of the knife shafts, and a wavy cut often results. In addition, when the cutting gap reaches its maximum in each revolution of the knives, the relatively soft material being cut is bent into the cutting gap and this results in a burr on the ribbon. Wavy cuts and burrs cause the opposite longitudinal edges of the ribbon to deviate out of parallel beyond permissible tolerances, and a burr also interferes with guidance of the ribbon through a head.
It is known to urge a cutting knife on one shaft elastically against a rigid knife on the other shaft for eliminating any cutting gap. However, previous arrangements for accomplishing this result in damaged ribbons of material intermediate acceptable ribbons. The damaged ribbons cannot be used and this waste of material cannot be accepted.